The present invention relates to lasers and particularly to electrically excited flowing gas lasers utilizing a gaseous lasing mixture.
In recent years, substantial progress has been made in the development of high power CO.sub.2 lasers in which the active gaseous medium flows through the working region in either the open or closed cycle CW or pulsed mode for flowing gas lasers or is sequentially replaced for the open or closed pulsed cycle mode of operation.
Electrically excited convection cooled CO.sub.2 lasers appear to offer the greatest potential for applications requiring either high average power or high peak power. The very high power capability of CO.sub.2 lasers (lasers however pumped using a gaseous lasing mixture including CO.sub.2) was first demonstrated, with the gas dynamic type which does not utilize electrical excitation or pumping. For a comprehensive discussion of the gas dynamic type laser including devices utilizing specific products of combustion, reference is made to U.S. Pat. No. 3,713,030, incorporated herein as if set out at length. See, also, "Gas Dynamic Lasers" by E. T. Gerry, American Physical Society Bulletin, Series II, Vol. 15, No. 4, p. 563, Apr. 1970 and "Gas Dynamic Lasers" by E. T. Gerry, IEEE Spectrum, pp. 51- 58, November 1970; and "Performance of an Unstable Oscillator on a 30 kW cw Gas Dynamic Laser" by E. V. Locke, R. Hella, and L. Westra, Avco Everett Research Laboratory, IEEE Journal of Quantum Electronics, Vol. QE-7, pp. 581- 583, December, 1971. However, electrically excited lasers and especially electrically excited convection cooled CO.sub.2 lasers appear to be better suited than gas dynamic lasers for many applications such as, for example, laser fusion work, heat treating, welding and cutting.
Of the many types of lasers under development such as, for example, the HF/DF lasers and CO lasers, CO.sub.2 lasers have the benefit of earlier and far greater development efforts. Further, over the past several years, research and development efforts have been concentrated on electrically excited convection cooled CO.sub.2 lasers operating in both the open and closed gas cycle mode. Such lasers that utilize a single large discharge volume appear to be best suited for use in high power laser systems because such lasers offer, among other things, a clear aerodynamic design, minimum ducting, low pressure loss in the laser channel, a uniform active medium and high output power.
For a description of one type of such laser, reference is made to U.S. Pat. No. 3,721,915 and for a detailed description of the electron beam-sustainer stabilized type laser, reference is made to U.S. Pat. No. 3,702,973, incorporated herein as if set out at length.
The output power of the above-noted electron beam-sustainer stabilized lasers have been made very large and can be made as large as one might reasonably desire. What is necessary in such lasers is the provision of efficient uniform and high power electrical excitation of the gas volume, a high energy density, and uniform optical quality. The electron beam-sustainer stabilized laser solves all of the above problems and can provide uniform electrical discharges in large gas volumes at from subatmospheric pressures to atmospheric pressure and above. At the volumes and pressures readily available with electron beam-sustainer stabilized lasers, application of an electric field alone to pump a lasable gas or gas mixture to produce a self-sustaining discharge in the gas quickly leads to formation of high-current constricted arcs.
In accordance with the teaching of the aforementioned U.S. Pat. No. 3,713,030, a plasma and especially a lasable gaseous mixture is stabilized through substantially its entire volume even at pressures greater than atmospheric by making the electron-ion production mechanism in the plasma independent of the electromagnetic field through the use of an external ionization source such as a large area, high energy electron beam. The separation of the electron-ion production mechanism from the applied electric field permits the electric field applied to be much lower than that otherwise required for self-sustaining discharges.
Thus, plasma stabilization by this technique permits large volumes of laser gas to be efficiently and effectively electrically pumped to produce optimum population inversion and high output power. Lasers operating in accordance with this technique not surprisingly have come to be called electron beam-sustainer stabilized lasers.
Electron beam-sustainer stabilized lasers are inherently capable of providing a very high output power. However, heretofore the production of such output power with such lasers required the provision of large volumes of laser gas comprising commercial grade carbon dioxide, nitrogen and helium. In the forms presently available, such gases not only are very costly per se, but also require substantial storage space depending on the rate of use and laser output power provided. Further, the storage means for these gases are very heavy, especially as compared to the weight of the gases alone.
In the present state of the art, gas dynamic lasers operating on combustion products as a working gas provide a specific energy of 10 kilojoules per pound of combustion fuel and a stored oxidizer or 35 kJ/lb when operated in an airbreathing mode using ambient oxygen as oxidizer without debit to the weight base. Chemical lasers (HF/DF) afford 300 kilojoules/lb of fluorine without considering pumping equipment and diluent gases and 10- 100 kJ/lb when taking such equipment into account. Prior art electric lasers employing CO.sub.2 :N.sub.2 :He working gas mixtures have a specific energy of 25 kJ/lb and 45kJ/lb when gases are precooled. The chemical and electrical systems require storage and transport of difficult to handle chemicals.
It is an important object of the present invention to reduce the operating cost of and/or enhance the logistical flexibility of laser apparatus.
It is a further object of the invention to reduce overall weight and/or volume of laser apparatus and associated operating accessories and supply materials consistent with the preceding object.
It is a further object of the invention to raise laser specific energy compared to the above-discussed prior art, consistent with one or more of the preceding objects.
It is a further object of the invention to utilize existing electrical controls, laser cavity defining equipment and developed operational methods consistent with one or more of the preceding objects.